In order to prevent the driver of a vehicle from falling asleep at the wheel, a device has been proposed for capturing a facial image of the driver using a camera mounted near the driver's seat and estimating the drowsiness of the driver based on a captured facial image (for example, in Patent Literature 1). This apparatus, using the captured facial image, measures a drowsiness characteristic quantity of the distance between a plurality of feature points (that is, feature regions on a face), the tilt of the head, or the like, and estimates the drowsiness based on the difference between the drowsiness characteristic quantity when awake (hereinafter sometimes referred to as “reference characteristic quantity”) and the drowsiness characteristic quantity when drowsiness is estimated.
The drowsiness determining device disclosed in Patent Literature 1, with regard to expression information indicating the distance and angle between various parts of the face, compares the expression information at a first timing and the expression information at a second timing, and judges the occurrence of drowsiness based of the magnitude relationship of the expression information.